# T2T: Tensor2Tensor Transformers

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[T2T](https://github.com/tensorflow/tensor2tensor) is a modular and extensible
library and binaries for supervised learning with TensorFlow and with support
for sequence tasks. It is actively used and maintained by researchers and
engineers within the Google Brain team.

We're eager to collaborate with you on extending T2T, so please feel
free to [open an issue on
GitHub](https://github.com/tensorflow/tensor2tensor/issues) or
send along a pull request to add your data-set or model.
See [our contribution
doc](CONTRIBUTING.md) for details and our [open
issues](https://github.com/tensorflow/tensor2tensor/issues).

---

## Walkthrough

Here's a walkthrough training a good English-to-German translation
model using the Transformer model from [*Attention Is All You
Need*](https://arxiv.org/abs/1706.03762) on WMT data.

```
pip install tensor2tensor

# See what problems, models, and hyperparameter sets are available.
# You can easily swap between them (and add new ones).
t2t-trainer --registry_help

PROBLEM=wmt_ende_tokens_32k
MODEL=transformer
HPARAMS=transformer_base

DATA_DIR=$HOME/t2t_data
TMP_DIR=/tmp/t2t_datagen
TRAIN_DIR=$HOME/t2t_train/$PROBLEM/$MODEL-$HPARAMS

mkdir -p $DATA_DIR $TMP_DIR $TRAIN_DIR

# Generate data
t2t-datagen \
  --data_dir=$DATA_DIR \
  --tmp_dir=$TMP_DIR \
  --problem=$PROBLEM

mv $TMP_DIR/tokens.vocab.32768 $DATA_DIR

# Train
# *  If you run out of memory, add --hparams='batch_size=2048' or even 1024.
t2t-trainer \
  --data_dir=$DATA_DIR \
  --problems=$PROBLEM \
  --model=$MODEL \
  --hparams_set=$HPARAMS \
  --output_dir=$TRAIN_DIR

# Decode

DECODE_FILE=$DATA_DIR/decode_this.txt
echo "Hello world" >> $DECODE_FILE
echo "Goodbye world" >> $DECODE_FILE

BEAM_SIZE=4
ALPHA=0.6

t2t-trainer \
  --data_dir=$DATA_DIR \
  --problems=$PROBLEM \
  --model=$MODEL \
  --hparams_set=$HPARAMS \
  --output_dir=$TRAIN_DIR \
  --train_steps=0 \
  --eval_steps=0 \
  --decode_beam_size=$BEAM_SIZE \
  --decode_alpha=$ALPHA \
  --decode_from_file=$DECODE_FILE

cat $DECODE_FILE.$MODEL.$HPARAMS.beam$BEAM_SIZE.alpha$ALPHA.decodes
```

---

## Installation

```
pip install tensor2tensor
```

Binaries:

```
# Data generator
t2t-datagen

# Trainer
t2t-trainer --registry_help
```

Library usage:

```
python -c "from tensor2tensor.models.transformer import Transformer"
```

---

## Features

* Many state of the art and baseline models are built-in and new models can be
  added easily (open an issue or pull request!).
* Many datasets across modalities - text, audio, image - available for
  generation and use, and new ones can be added easily (open an issue or pull
  request for public datasets!).
* Models can be used with any dataset and input mode (or even multiple); all
  modality-specific processing (e.g. embedding lookups for text tokens) is done
  with `Modality` objects, which are specified per-feature in the dataset/task
  specification.
* Support for multi-GPU machines and synchronous (1 master, many workers) and
  asynchrounous (independent workers synchronizing through a parameter server)
  distributed training.
* Easily swap amongst datasets and models by command-line flag with the data
  generation script `t2t-datagen` and the training script `t2t-trainer`.

---

## T2T overview

### Datasets

**Datasets** are all standardized on `TFRecord` files with `tensorflow.Example`
protocol buffers. All datasets are registered and generated with the
[data
generator](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/bin/t2t-datagen)
and many common sequence datasets are already available for generation and use.

### Problems and Modalities

**Problems** define training-time hyperparameters for the dataset and task,
mainly by setting input and output **modalities** (e.g. symbol, image, audio,
label) and vocabularies, if applicable. All problems are defined in
[`problem_hparams.py`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/data_generators/problem_hparams.py).
**Modalities**, defined in
[`modality.py`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/utils/modality.py),
abstract away the input and output data types so that **models** may deal with
modality-independent tensors.

### Models

**`T2TModel`s** define the core tensor-to-tensor transformation, independent of
input/output modality or task. Models take dense tensors in and produce dense
tensors that may then be transformed in a final step by a **modality** depending
on the task (e.g. fed through a final linear transform to produce logits for a
softmax over classes). All models are imported in
[`models.py`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/models/models.py),
inherit from `T2TModel` - defined in
[`t2t_model.py`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/utils/t2t_model.py)
- and are registered with
[`@registry.register_model`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/utils/registry.py).

### Hyperparameter Sets

**Hyperparameter sets** are defined and registered in code with
[`@registry.register_hparams`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/utils/registry.py)
and are encoded in
[`tf.contrib.training.HParams`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/contrib/training/python/training/hparam.py)
objects. The `HParams` are available to both the problem specification and the
model. A basic set of hyperparameters are defined in
[`common_hparams.py`](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/models/common_hparams.py)
and hyperparameter set functions can compose other hyperparameter set functions.

### Trainer

The **trainer** binary is the main entrypoint for training, evaluation, and
inference. Users can easily switch between problems, models, and hyperparameter
sets by using the `--model`, `--problems`, and `--hparams_set` flags. Specific
hyperparameters can be overriden with the `--hparams` flag. `--schedule` and
related flags control local and distributed training/evaluation
([distributed training documentation](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/docs/distributed_training.md)).

---

## Adding a dataset

See the [data generators
README](https://github.com/tensorflow/tensor2tensor/tree/master/tensor2tensor/data_generators/README.md).

---

*Note: This is not an official Google product.*